I don't think letters really matter (no matter what anybody says, including the actors). What will matter is ratings/focus groups/etc. If the ratings don't go down (or even go up) while Bo is gone and TPTB get good feedback from whatever is going on with Hope and/or Carly while Bo is gone, then they'll know they can get away with sending Bo to Downtown Europe or Africa or just having him "in Salem" but never seen.